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CKSUM(1)                FreeBSD General Commands Manual               CKSUM(1)

NAME
     cksum, sum - display file checksums and block counts

SYNOPSIS
     cksum [-o 1 | 2 | 3] [file ...]
     sum [file ...]

DESCRIPTION
     The cksum utility writes to the standard output three whitespace
     separated fields for each input file.  These fields are a checksum CRC,
     the total number of octets in the file and the file name.  If no file
     name is specified, the standard input is used and no file name is
     written.

     The sum utility is identical to the cksum utility, except that it
     defaults to using historic algorithm 1, as described below.  It is
     provided for compatibility only.

     The options are as follows:

     -o      Use historic algorithms instead of the (superior) default one.

             Algorithm 1 is the algorithm used by historic BSD systems as the
             sum(1) algorithm and by historic AT&T System V UNIX systems as
             the sum(1) algorithm when using the -r option.  This is a 16-bit
             checksum, with a right rotation before each addition; overflow is
             discarded.

             Algorithm 2 is the algorithm used by historic AT&T System V UNIX
             systems as the default sum(1) algorithm.  This is a 32-bit
             checksum, and is defined as follows:

                   s = sum of all bytes;
                   r = s % 2^16 + (s % 2^32) / 2^16;
                   cksum = (r % 2^16) + r / 2^16;

             Algorithm 3 is what is commonly called the `32bit CRC' algorithm.
             This is a 32-bit checksum.

             Both algorithm 1 and 2 write to the standard output the same
             fields as the default algorithm except that the size of the file
             in bytes is replaced with the size of the file in blocks.  For
             historic reasons, the block size is 1024 for algorithm 1 and 512
             for algorithm 2.  Partial blocks are rounded up.

     The default CRC used is based on the polynomial used for CRC error
     checking in the networking standard ISO 8802-3: 1989.  The CRC checksum
     encoding is defined by the generating polynomial:

           G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
                x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1

     Mathematically, the CRC value corresponding to a given file is defined by
     the following procedure:

           The n bits to be evaluated are considered to be the coefficients of
           a mod 2 polynomial M(x) of degree n-1.  These n bits are the bits
           from the file, with the most significant bit being the most
           significant bit of the first octet of the file and the last bit
           being the least significant bit of the last octet, padded with zero
           bits (if necessary) to achieve an integral number of octets,
           followed by one or more octets representing the length of the file
           as a binary value, least significant octet first.  The smallest
           number of octets capable of representing this integer are used.

           M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided
           by G(x) using mod 2 division, producing a remainder R(x) of degree
           <= 31.

           The coefficients of R(x) are considered to be a 32-bit sequence.

           The bit sequence is complemented and the result is the CRC.

EXIT STATUS
     The cksum and sum utilities exit 0 on success, and >0 if an error occurs.

SEE ALSO
     md5(1)

     The default calculation is identical to that given in pseudo-code in the
     following ACM article.

     Dilip V. Sarwate, "Computation of Cyclic Redundancy Checks Via Table
     Lookup", Communications of the Tn ACM, August 1988.

STANDARDS
     The cksum utility is expected to conform to IEEE Std 1003.2-1992
     (``POSIX.2'').

HISTORY
     The cksum utility appeared in 4.4BSD.

FreeBSD 11.0-PRERELEASE         April 28, 1995         FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | SEE ALSO | STANDARDS | HISTORY

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